Kites

ABSTRACT

The wind-formed flexible kite is improved by the use of two longitudinal ribs supporting the flexible surface which are elastically bowed in flight. This structure produces a kite which billows open reliably under all flight conditions and which thereby permits wind formed kites to be designed in a greater variety of sizes and configurations with resulting increases of flight stability and efficiency.

United States Patent 11 1 1111 3,767,145 Holland, Jr. 1 1 Oct. 23, 1973 [54] KITES 3,055,622 9/1962 Harmon 244/l53 R [76] Inventor: Raymond Prunty Holland, Jun, 1702 FOREIGN PATENTS OR APPLICATIONS Th'rd ROSWell, 448,320 1 1913 France 244 154 8820] [22] Filed: Oct. 29, 1971 Primary Examiner-Milton Buchler Assistant ExaminerPaul E. Sauberer [211 APPL 193,875 Attorney-Raymond PfiihtfiiflfidJr.

52 us. (:1 244/153 R 15 ABSTRACT [51] Int. Cl. B64c 31/06 The w1nd-formed flexible kite is improved by the use {58] new of Search 244/153 155 R of two longitudinal ribs supporting the flexible surface which are elastically bowed in flight. This structure [56] Reierences cued produces a kite which billows open reliably under all UNITED STATES PATENTS flight conditions and which thereby permits wind 2,071,807 2/1937 Wolff 244/153 R formed kites to be designed in a greater variety of 2,394,366 2/1946 etal- 244/53 R sizes and configurations with resulting increases of 2,537,560 1 1951 wahner........ 244 153 R flight Stability and efficiency 5 2,737,360 3/1956 1 Allison 244/153 R 5 Claims, 7 Drawing Figures KITES The present invention relates to improvements in flexible wind-formed kites of the general type now sold under the trademark name Scott Sled, or as described by Allison in US. Pat. No. 2,737,360. Kites Of this sort consist of a non-rigid sail stiffened by two or more longitudinal ribs. They achieve their flight form by billowing open in the wind in the manner of a parachute.

In the past, flexible wind-formed kites have had shortcomings: They cannot be made small, nor in any substantial variation from a few forms known by trail to be successful, without becoming aerodynamically unstable and suffering a tendency to collapse. The use of numerous bridle lines, such as taught by Rogallo in US. Pat. No. 2,546,078 to preserve the desired windinflated form, or the use of a spreader bar across the open mouth of the kite, as often advocated, do not solve these problems because a wind-formed kite must be able to recover its form after being turned inside out. This occurs sooner or later due to a severe reverse gust. When such reversal occurs, any bridal line in excess of two, or a spreader bar near the kite, will foul the bridle, preventing full billowing and causing the kite to fall.

Before this invention the kite designer was seriously hampered by the tendency of the wind-formed kite to lose its fully billowed form or to collapse locally at the leading edge. It was considered normal for an expermental kite to collapse in gusty air. Even kites of proven design did not billow fully, allowing the two branches of the bridle to twist around each other, sometimes causing one branch of the bridle to shorten more than the other. This destroys symmetrical trim, causing the kite to descend to one side, and bridle twisting always closes the open mouth of the kite somewhat, causing an increased tendency for billowing to falter, often leading progressively to a failure of billowing and a collapsed kite, falling to the ground. The use of a mechanical swivel to prevent the twist-up of the bridle has proven largely ineffective in flight because of friction.

The present invention solves these difficulties, and makes possible improved flight stability, and performance, in a widened variety of kite forms and sizes. The objects of this invention are:

Toproduce a flexible kite which billows open in the wind regardless of the degree of gustiness of the wind or the size of the kite.

To produce a flexible kite which is aerodynamically stable, even when constructed in an unusually small size.

To provide a positive mouth-opening action on a flexible kite to obtain and maintain an open billowing form, and to do so without adding extra parts,.and without sacrificing the existing ability. of the flexible kite to reverse itself in flight without tangling.

To produce aerodynamic forces on a flexible kite which hold the windward mouth of the kite open and resist the tendency of the bridle lines to twist around each other, an action which would otherwise tend to collapse the kite and destroy its ability to fly.

To produce a type of flexible kite which allows increased latitude for the designer, enabling him to design kites having relatively longer spans and narrower chords, thereby achieving steeper flight angles, higher 2 flights, improved weight lifting ability and lighter string pulls, and enabling him to design in a wide variety of forms and sizes, without encountering unsatisfactory billowing action or unsatisfactory aerodynamic stability.

FIGS. 1 and 2 illustrate prior art, showing the Allison and Scott Sled kites, respectively, in flight.

FIG. 3 shows a kite of the present invention in flight.

FIGS. 4 through 7 show kites of the present invention, not in flight, placed in flat positions. All are stretched out laterally except the kite of FIG. 5, which is relaxed.

FIGS. 4 and 5 show a kite on which the longitudinal ribs are attached to the sail by means of tape.

FIG. 6 shows a kite on which the longitudinal ribs are attached by being threaded through holes in the sail.

FIG. 7 shows four of the many alternative forms of the flexible wind-formed kite available to the designer of kites of the present invention.

In every figure the front edge of the kite, the leading edge, is at the top of the figure. The longitudinal direction is vertically toward the top of the sheet, or close to it, and the lateral direction is cross-wise on the sheet, perpendicular to the longitudinal direction.

In the prior art, the longitudinal ribs which support the flexible sail have always been straight, and so attached to the flexible sail that they remain straight in flight. In the present invention these ribs are curved, producing very marked benefits. Specifically, in this invention the two longitudinal ribs which are located at the inboard ends of the two lapels (the lapels being the tapered lateral extremities of the kite) are mounted on the kite so as to be curved in flight. It serves the purposes of definition to observe that these ribs are mounted so as to be concave inwardly (concave towardeach other) when the kite, not in flight, is stretched out flat laterally. These longitudinal ribs are preferably elastic spring-like members which straighten out when the kite is not stretched sideways. In small kites, straight slender birch dowels are often used as supporting ribs. Other kinds of ribs also produce the desired results to a worthwhile degree even if they are permanently bowed members or are closed pressure-inflated tubes, so long as they have the inwardly concave form as defined above.

When the kite is in flight, billowing full in the wind like a parachute, with its open side facing in a direction between the downward direction and the windward direction, the presence of the curved ribs causes the upper or leading edge of the kite and the lower or trailing edge of the kite to be raised relative to the midsection. The kite is given a small amount of nose-up camber. This may be seen by observing that the curved ribs are now located largely on the sides of the kite. See FIG. 3. The ribs themselves are now concave upwardly. In this manner, the leading edge of the kite is made to rise, for well known aerodynamic reasons, and the open face of the kite is presented more steeply to the wind, keeping the kite billowing full.

The action of flexibility in the curved ribs further improves billowing. There is always some tendency for ribs 2 to straighten, an action which is greatest when the wind is the lightest and least when the wind is strongest. To the same degree that ribs 2 straighten, the free edges of the lapels of the kite slacken, and billow outwardly, giving the kite its necked-down or corset-like form. See FIG. 3. This form, when viewed by the kite flier looking up the string, is broader at the upwind and downwind ends of the kite than it is between these ends. The narrowest part of the corset-like form occurs close to the points on the kite where the two branches of the bridle are attached. The form, as compared to that of a kite of the prior art, a kite having straight stiffeners but otherwise identical, has a widened upwind mouth and a widened downwind skirt, and is narrowed between, in a moderate but distinct hourglass form. See FIG. 3.

This form having been achieved in flight, the aerodynamic action which improves billowing is as follows: Observe the two lapel regions of the kite, each ofa generally triangular form, at the two sides of the kite, lying between the ribs and the points at which the bridles attach. As a part of the overall corset-like form, each of these lapels takes a form which is cambered, concave outwardly. See the sides of the kite in FIG. 3. Each lapel stands downwardly at the side of the kite, positioned close to the vertical direction. Due to its cambered form each of these lapels experiences a pitching moment" (in airfoil terminology) and due to the lapel position this moment is in a direction to open the upper or forward, or windward end of the kite. Each lapel is twisted by aerodynamic forces in the direction which causes its front edge to open outward, holding the mouth of the kite open. Because its mouth is held open in this manner, the kite stays billowed open.

Flight tests have shown that even a very small amount of bend in the longitudinal ribs produces marked benefits in keeping the kite open, as little as one-eighth inch of bend in eighteen inches having clearly observable benefits. A larger bend than this is used ordinarily to provide a margin of safety.

The benefit of springiness in the rib occurs most strikingly when the wind slackens most, perhaps due to a reverse-direction gust, perhaps causing the kite to go entirely slack and fall like a leaf, folded double. In this extreme condition. ribs 2 straighten completely. Then, as the wind resumes, aerodynamic forces resume on the kite which produce at least a small amount of tension in the flying line. This tension is transmitted to the kite through the two branches of the bridle, directly to the midsections of the straightened ribs, the material of the sail between the bridle tie points and the midsections of the ribs having been pulled out taut by the straightening of the rib. lmportantly, the straightening of the rib in this condition leaves the leading and trailing edges of the lapels entirely limp and slack. See FIG. 5. These limp edges of the lapels, both forward and rearward of the bridle tie points, are blown outward, spreading the open side of the kite, causing billowing to proceed at once to fullness.

The kite form is more open-mouthed where the bridle does not attach than it is where the bridle does attach. The two branched bridle of any wind-formed kite must always pull so as to close the kite mouth somewhat. This invention limits such unavoidable closing to a small mid section and correspondingly reduces the closing effect.

The spring-like ribs also prevent the collapse of the leading edge of the central part of the kite. In any degree of slackened wind, as the spring-like ribs straighten, the central sail of the kite between the ribs and between the leading and trailing edges tends to go slack. Whatever tension remains across the sail is transmitted principally to the leading edge of the sail and secondarily to the trailing edge of the sail. So long as tension remains in the leading edge, produced in this manner, the leading edge does not blow back. See FlG. 5.

Spring-like ribs keep the leading edge of the main sail in tension so that it does not collapse and so that it holds any pressure available from the wind, and they cause the edges of the lapels to go slack as the wind slackens, so that the lapels billow outwardly in response to the pressure from the main sail, thereby holding the kite open so long as any wind at all is present. These benefits of the spring-like ribs apply most strongly in any temporary slackening of the wind, and of course they also apply when launching the kite, when the kite must open up and billow in the lightest of breezes.

Conventional kites of the billowing type have a strong tendency to collapse and to fail to billow when they are very small, or when they are of a form having a narrow chord and wide span, or when they are made in other unconventional forms. By correcting these deficiencies by the means described here, these limitations are removed, with obvious advantages, either for kite-flying for sport or for economic benefits from kite manufacturing and sales.

Similarly, conventional billowing kites that are small, or of unconventional form, have a tendency to be aerodynamically unstable, typically gyrating in circles at the end of the flying line. Through the actions of the corsetlike form, the cambered lapels, and the spring-like ribs, described above, an increase of restoring moments and an increase of aerodynamic damping are achieved, greatly reducing these stability problems, so that billowing kites of unusually small size and unconventional form may be made having adequate stability.

This invention opens a bag of tricks for the kite designer, whether the kite is very small or very large. The amount of bend employed in the longitudinal stiffeners, their degree of stiffness and the positioning of these stiffeners permits the kites to take a variety of shapes. The nose-up pitching moment imparted to the kite by its curved ribs permits the bridle tie points and the center of gravity of the kite to be moved somewhat forward, with stability advantages. On very large kites, the longitudinal stiffener is typically a laminated wooden spar, the in-flight deflection curve of which may be tailored to achieve particular results. The spar may be tapered, with different section moments of inertia at different stations and in different planes. Such a spar may be designed to roll over somewhat when pulled into a bent form by the tension of the sail, producing a resilient flight form having the proper distribution of tension in the sail to produce the desired trim and billowing properties.

Now, referring specifically to the drawing, FIGS. 1 and 2 show conventional billowing kites, each employing three straight supporting ribs, in flight. These kites lack the curved supporting ribs and corset-like form of kites of this invention. They can take only those forms into which a flat sheet of paper can be bent, and completely lack purposeful compound curvature. On these conventional kites the tension in the bridle pulls the entire mouth of the kite closed somewhat.

In FIG. 3 a kite of this invention is shown in flight, having flexible sail l and supporting ribs 2. The form produced has compound curvature, bulging and draping to produce flight benefits. The mild corset-like form may be seen. Observe the concave sides of the kite. The

mouth-closing tendency due to bridle tension is diminished by being present only locally.

In FIG. 4 the kite of FIG. 3 is laid out on a flat surface and is stretched out laterally. Supporting ribs 2 are bowed concave inwardly, and are attached to flexible sail l by pressure sensitive adhesive tapes 3a, 3b, and 3c. Reinforcing tapes are also shown at the forward ends of ribs 2 and at the bridle tie points. The use of tapes in this manner permits the use of very light film for sail 1, desirable for obtaining compound curvature, and with additional advantages in increasing the stability and reducing the weight of the kite.

In FIG. 5, the supporting ribs 2 are spring-like members which straighten when they are relaxed. The kite in FIG. 5 is lying on a flat surface as in FIG. 4, but it is not stretched out laterally, and ribs 2 have straightened. It may be seen how this straightening of the ribs causes the leading and trailing edges of the lapels (outboard of ribs 2) and the central portion of the main sail (between the mid sections of ribs 2) to go slack, and causes tautness to remain at the leading edge 11 and trailing edge 12 of the main sail and along a direct line from the lateral extremities of the lapel to the mid sections of the straightened ribs. This distribution of tautness and slackness produces the desirable actions causing the kite to open in slackened winds, as described above, and the curved ribs as seen in FIG. 4 cause the kite to remain open once billowing full.

In FIG. 6, an alternate means of attachment of the longitudinal ribs 2 to sail l is shown. The ribs are thin wooden dowels, slotted at the ends, threaded through slots 4 in the material of the flexible sail l, and engaged at their slotted ends in slots 5a and 5b. This construction has particular advantages for producing an inexpensive kite.

In a variation, not shown, a conventional border string could be attached around the perimeter of the kite material, and stiffeners 2 could engage this border string in the slotted ends. Slots 6 are located at the lateral extremities of lapels 7, to receive the ends of the two branches of flying bridle 8. At the central point of bridle 8 loop 9 is located for attachment to flying line 10.

In FIG. 7, several unconventional forms of billowing kites are shown, as made stable and capable of billowing by this invention. The construction in FIGS. 7A uses two longitudinal ribs, whereas the constructions in FIGS. 78 and 7C each use three longitudinal ribs. The kite in FIG. 7D uses four longitudinal ribs, two of which are located at the lateral extremities of the lapels. In FIG. 7A the sail material at the lateral extremities of the lapels is locally necked down and is wide again at ear l1 outboard of the necked down region. This construction is an alternative to slot 6, and is for the purpose of making a strong attachment of the bridle lines to the sail, by wrapping the bridle line around the necked-down region and tying it there. The kite in FIG.

7B has an internal hole in the manner of the Scott Sled, and the kites in FIGS. 7A and 7B employ scalloped edges. The function of the internal hole is to relieve pressure relatively toward the rear of the kite, in order to maintain a relatively greater pressure forward, to hold the forward portions spread apart, to assist billowmg.

The functions of the scalloping are to prevent leading edges from blowing back and to prevent flapping of edges, and also to reduce aerodynamic drag.

The kite forms shown in FIG. 7 achieve relatively long wing span and relatively narrow wing chord, accomplishing relatively high aerodynamic aspect ratio. This produces benefits in kite performance: A steepened flight angle and a relatively light string pull. The light string pull in turn allows a thinner string to be used which produces a still steeper flight angle, so that substantial cumulative benefits are achieved.

It may be seen in FIGS. 4, 6 and 7 that the front ends of ribs 2 have a toed-in position, opposite from the toed-out" positions of the stiffeners illustrated on the Allison kite in FIG. 1. One might intuitively expect such toed-in members to cause the sides of the kite to be driven toward each other causing the kite to collapse. The reverse is true, as described and explained above.

I claim:

1. A flexible wind-formed kite comprising a flexible sail of generally symmetrical form having its axis of symmetry lying in the longitudinal direction, and having supporting ribs lying in generally longitudinal positions attached to said sail, said supporting ribs comprising two ribs attached symmetrically to said sail on opposite sides of said longitudinal axis of symmetry, each of said symmetrically placed supporting ribs having a bowed form, said form being bowed laterally, concave inwardly, when said flexible sail is placed in a flat position, stretched out laterally, said sail having a flexible leading edge, a portion of said leading edge being situated between the front ends of said inwardly concave supporting ribs.

2. The kite of claim 1, said supporting rib being a thin resilient spring-like member.

3. The kite of claim 1 comprising two cord attachment points located symmetrically opposite each other near the lateral extremities of said sail.

4. The kite of claim 3 comprising a symmetrical V- shaped bridle of cord-like material the outer extremities of said bridle being attached at said cord attachment points, said bridle comprising an additional cord attachment point at the central point thereof for attaching the flying line to said bridle.

5. The kite of claim 1, the portion of said sail located outboard of said supporting ribs being of generally triangular lapel-like form. 

1. A flexible wind-formed kite comprising a flexible sail of generally symmetrical form having its axis of symmetry lying in the longitudinal direction, and having supporting ribs lying in generally longitudinal positions attached to said sail, said supporting ribs comprising two ribs attached symmetrically to said sail on opposite sides of said longitudinal axis of symmetry, each of said symmetrically placed supporting ribs having a bowed form, said form being bowed laterally, concave inwardly, when said flexible sail is placed in a flat position, stretched out laterally, said sail having a flexible leading edge, a portion of said leading edge being situated between the front ends of said inwardly concave supporting Ribs.
 2. The kite of claim 1, said supporting rib being a thin resilient springlike member.
 3. The kite of claim 1 comprising two cord attachment points located symmetrically opposite each other near the lateral extremities of said sail.
 4. The kite of claim 3 comprising a symmetrical V-shaped bridle of cord-like material the outer extremities of said bridle being attached at said cord attachment points, said bridle comprising an additional cord attachment point at the central point thereof for attaching the flying line to said bridle.
 5. The kite of claim 1, the portion of said sail located outboard of said supporting ribs being of generally triangular lapel-like form. 